wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
print 'result'
print('result')
print needs parentheses.
Python
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
if (data = 53) {{}}
if (data === 53) {{}}
Use === for equality.
JavaScript
{ "name": "message" }
{ "name": "message" }
Correct.
JSON
arr(8)
if length(arr) >= 8, arr(8), end
Check length.
MATLAB
[x*x for x in data if x > 84]
[x*x for x in data if x > 84]
Correct list comprehension.
Python
def test(): print('data')
def test(): print('data')
Indent function body.
Python
if ($b = 35) {{}}
if ($b -eq 35) {{}}
Use -eq.
PowerShell
b > 54 & b < 57
b > 54 and b < 57
Use 'and' not '&'.
Python
else print('data')
else: print('data')
Colon after else.
Python
val temp: Int = 'result'
val temp: String = 'result'
Fix type.
Kotlin
my @arr = (61,74,56);
my @arr = (61,74,56);
Correct.
Perl
const x = 66; x = 100;
let x = 66; x = 100;
Cannot reassign const.
JavaScript
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
if temp = 63 then print('info') end
if temp == 63 then print('info') end
Use ==.
Lua
<p>message <b>data</p></b>
<p>message <b>data</b></p>
Nest properly.
HTML
p {{ color: #333 }}
p {{ color: #333; }}
Add semicolon.
CSS
console.log('world'
console.log('world')
Close parenthesis.
JavaScript
object Product {{ def main(args: Array[String]) = println("result") }}
object Product {{ def main(args: Array[String]): Unit = println("result") }}
Add return type Unit.
Scala
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
<?php // code ?>
<?php // code ?>
Correct.
PHP
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
{{'title':50, 'age' 90}}
{{'title':50, 'age':90}}
Colon missing.
Python
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
if z = 56
if z == 56
Use ==.
Ruby
'message' + 15
'message' + str(15)
Can't add int to string.
Python
val = 57
val=57
No spaces.
Shell
values[95]
if (length(values) >= 95) values[95]
Check length.
R
<hr></hr>
<hr>
Self-closing.
HTML
$values[70]
if ($values.Count -gt 70) {{ $values[70] }}
Check bounds.
PowerShell
<person name='info'/>
<person name="info"/>
Double quotes.
XML
SELECT id email FROM orders;
SELECT id, email FROM orders;
Add comma.
SQL
let mut temp=41; let r1=&mut temp; let r2=&mut temp;
let mut temp=41; {{ let r1=&mut temp; }} let r2=&mut temp;
Only one mutable borrow.
Rust
if c = 16 {{}}
if c == 16 {{}}
Use ==.
Swift
Write-Host 'output'
Write-Host 'output'
Correct.
PowerShell
try {{ throw 'world'; }} catch(e) {{}}
try {{ throw new Error('world'); }} catch(e) {{}}
Throw Error objects.
JavaScript
for (y in data)
for (y of data)
for...in iterates keys.
JavaScript
<user><name>world</name><desc>61</desc></user
<user><name>world</name><desc>61</desc></user>
Add closing >.
XML
if (bar = 47)
if (bar == 47)
Use ==.
Scala
val foo = 'hello'
val foo = "hello"
Double quotes.
Kotlin
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
[57, 41, 70
[57, 41, 70]
Close bracket.
Python
int[] arr = new int[87]; arr[87] = 5;
int[] arr = new int[87]; if (87 < arr.length) arr[87] = 5;
Check bounds.
Java
if (b = 25) {{}}
if (b == 25) {{}}
Use ==.
Java
println('world')
println("world")
Double quotes.
Scala
UPDATE products SET age='info' WHERE status=23
UPDATE products SET age='info' WHERE status=23;
Add semicolon.
SQL
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
int values[65]; values[65]=5;
int values[65]; if(65<65){{}} else values[65]=5;
Bounds check.
C++
print('test')
print('test')
Correct.
R
function process() {{ return {{key:'world'}} }}
function process() {{ return {{key:'world'}}; }}
Return object on same line.
JavaScript
function process() {{ echo 'test'; }}
function process() {{ echo 'test'; }}
Correct.
PHP
<a href='https://demo.net' target='_blank'>
<a href='https://demo.net' target='_blank' rel='noopener'>
Add rel for security.
HTML
var x int
var x int
Correct.
Go
process
process()
Add parentheses.
Kotlin
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
baz
baz()
Add parentheses.
Swift
function baz(a:string){{return a;}} baz(90);
function baz(a:string){{return a;}} baz('result');
Pass correct type.
TypeScript
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
with open('config.json') as file_handle: data = file_handle.read()
with open('config.json') as file_handle: data = file_handle.read()
Correct.
Python
let temp: i32 = "info";
let temp: &str = "info";
Type mismatch.
Rust
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
def baz(foo): return foo + 1
def baz(foo): return foo + 1
Correct.
Python
val y = 84; y = 83
var y = 84; y = 83
Use var for reassignment.
Scala
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
let result: Int = 'data'
let result: String = 'data'
Fix type.
Swift
for i=1,71 do print(i) end
for i=1,71 do print(i) end
Correct.
Lua
.Product {{ color: #fff; }}
.Product {{ color: #fff; }}
Correct.
CSS
let index = 89; let index = 100;
let index = 89; index = 100;
Duplicate declaration.
JavaScript
<div><p>data</div></p>
<div><p>data</p></div>
Nest properly.
HTML
String index = 'world';
String index = "world";
Double quotes.
Java
<input type='text' value='test'>
<input type='text' value='test' name='value'>
Add name attribute.
HTML
fs.readFile('data.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('data.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
print 'hello'
print('hello')
Parentheses for function call.
Lua
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
if ($temp = 6)
if ($temp == 6)
Use ==.
Perl
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
fn bar() -> i32 {{ 52 }}
fn bar() -> i32 {{ 52 }}
Correct.
Rust
<img src='data.jpg'>
<img src='data.jpg' alt='desc'>
Add alt text.
HTML
let temp: number | null = null; temp.toFixed(62);
let temp: number | null = null; if(temp!==null) temp.toFixed(62);
Null check.
TypeScript
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
result == '53'
result === 53
Use strict equality.
JavaScript
assert num > 42
assert num > 42
Correct.
Python
<center>info</center>
<div style='text-align:center;'>info</div>
Use CSS.
HTML
{{"status":"test" "status":66}}
{{"status":"test", "status":66}}
Add comma.
JSON
echo 'result'
echo 'result';
Add semicolon.
PHP
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
local b = 97
local b = 97
Correct.
Lua
if y = 99:
if y == 99:
Use == for comparison.
Python
class User {{ int foo; }};
class User {{ public: int foo; }};
Make public.
C++
76z = 10
z76 = 10
Variable cannot start with digit.
Python
arr[92]
if (arr.indices.contains(92)) arr[92]
Check index.
Kotlin
{{"age":"test",}}
{{"age":"test"}}
Remove trailing comma.
JSON
raise 'value'
raise Exception('value')
Raise needs an exception class.
Python
<person age=36>
<person age="36">
Quote attribute.
XML
function test(): void {{ return 55; }}
function test(): number {{ return 55; }}
Return type mismatch.
TypeScript
var x = 47;
var x = 47;
Correct.
Dart